Compact fiber-optic detector-array-based spectrometers (“miniature spectrometers”) pioneered by H.-E. Korth of IBM Germany and popularized most notably by Ocean Optics, Inc. have found widespread use in a multitude of applications due to their low cost, small size, and low power consumption compared to conventional spectrometers. The purpose of these spectrometers is to measure the intensity of light as a function of wavelength. For example, see “A Computer Integrated Spectrophotometer for Film Thickness Monitoring,” H.-E. Korth, IBM Germany, JOURNAL DE PHYSIQUE, Colloque CIO, Supplement Number 12, Tome M, December 1983, pg. C10-101.
Oftentimes such a spectrometer is used in a system that characterizes a material by analyzing how the material interacts with light over a range of wavelengths. Common examples are reflectance and transmittance measurement systems. Such systems require a light source to generate the light that is eventually analyzed by the spectrometer.
The type of light source that is used with a miniature spectrometer depends primarily on the wavelength range of the spectrometer. For ultraviolet wavelengths (below ˜380 nm) a deuterium light source (e.g., Hamamatsu L10290) is generally used. In some limited cases (e.g., color measurements) when only visible wavelengths (450-700 nm) are of interest a white-light LED can be used. However, the majority of miniature spectrometer applications fall within the 380-2200 nm wavelength range, where an incandescent source is nearly always used. By far the most common incandescent source used with miniature spectrometers is a tungsten-halogen lamp, e.g., the LS-1 from Ocean Optics, Inc.
Incandescent light sources are widely used for broadband applications because they are relatively stable, bright, and inexpensive. However, they do require a considerable amount of power to operate; the lamp in the aforementioned Ocean Optics LS-1 uses 6.5 W, for example. This is on the order of fifty times more power than is required to operate a typical miniature spectrometer. This not only greatly restricts the length of time that battery-powered incandescent-based miniature spectrometer systems can operate on a single charge, but it also prevents such systems from being powered through a Universal Serial Bus (USB) cable (which is limited to 2.25 W power draw).